DETROIT -- Picking up right where they left off, Donald Trump, Ted Cruz and Marco Rubio barked out fresh insults at each other in a Republican presidential debate Thursday night that also featured a crude sexual reference from Trump -- and a healthy dose of policy, too.

Cruz and Rubio, who earlier had devoted considerable debate time to throwing sharp elbows at one another, were relentless in training their fire on Trump.

Rubio justified his attacks on Trump by saying the billionaire businessman had "basically mocked everybody" over the past year. Trump countered with a feint, saying he'd called Rubio a "lightweight" in the past but "he's really not that much of a lightweight."

Trump then noted that Rubio had mocked his hands as small, widely viewed as an insult about Trump's sexual prowess. Holding his hands up to the audience, Trump declared, "I guarantee you, there's no problem" in that area.

It was a jaw-dropping moment in a campaign that's been full of surprises from the beginning.

For all of the criticism and ill will, Cruz, Rubio and Kasich all said they would support Trump if he is the Republican nominee. He, too, said he would support whoever wins.

There was plenty of policy, too, as Rubio and Cruz pressed Trump aggressively on his conservative credentials, his business practices and shifting policy positions.

Trump, in short order, acknowledged his willingness to deal and be flexible when it suits his needs.

He said it was fine that Rubio had negotiated with other lawmakers on immigration policy.

He said he had changed his own mind to support admitting more highly skilled workers from overseas, saying matter-of-factly, "I'm changing. I'm changing. We need highly skilled people in this country."

And he also was matter of fact about providing campaign contributions to leading Democrats, including 10 checks to Hillary Clinton, reviled by many conservatives.

Trump said it was simply business.

"I've supported Democrats and I've supported Republicans, and as a businessman I owed that to my company, to my family, to my workers, to everybody to get along," he said.

When moderator Megyn Kelly told Trump his shifts caused some people to question his core, Trump insisted: "I have a very strong core. I have a very strong core. But I've never seen a successful person who wasn't flexible, who didn't have a certain degree of flexibility."

John Kasich sought to turn Trump's statement on the value of "flexibility" into a character question. When the Ohio governor meets with voters, he said, "you know what they really want to know? If somebody tells them something, can they believe it?

Rubio chimed in, "When they're done with the yoga, can I answer a question?"

In one particularly sharp exchange, Rubio renewed his criticisms of Trump University, which charged students $1,495 each for seminars that would teach them the billionaire's secrets to making it big in real estate. A lawsuit filed by the New York attorney general claims the classes fell so short of promises that it amounted to fraud.

"He's trying to do to the American voters what he did to the people that signed up for this course," Rubio declared. "He's trying to con people into giving him their vote just as he conned those people."

Cruz, tag-teaming on the issue, saying, "If we nominate Donald, we're going to spend the fall and the summer with the Republican nominee facing a fraud trial,"

And he turned the tables, saying Rubio is "the real con artist." He said the first-term senator "scammed the people of Florida" by skipping a high number of votes while running for president.

In another exchange, Rubio faulted Trump's businesses for manufacturing clothing in China and Mexico rather than the U.S.

Trump retorted, "This little guy has lied so much about my record."

Asked when he would start making more clothes in the U.S., Trump said that would happen when currency valuations weren't biased against manufacturing garments in America.

Cruz, too, took the fight to Trump, accusing him of being "someone who has used government power for private gain."

"For 40 years, Donald has been part of the corruption in Washington" that people are angry about, Cruz said, citing Trump's campaign contributions to leading Democrats, including then-Sen. Clinton.

Trump piled more insults, too, on the party's 2012 presidential nominee, Mitt Romney, who earlier Thursday made a rare public appearance to denounce Trump as "a phony" who is "playing the American public for suckers."

Trump dismissed Romney as "a failed candidate" and an "embarrassment."

"Obviously, he wants to be relevant," Trump said dismissively.

Thursday's debate was the first time he faced questioning from Kelly since the two clashed in the first primary debate. That's when Kelly's tough questioning about Trump's treatment of women blew up into a running argument between Fox and the candidate.

Trump signaled he was ready for a truce. When Kelly posed her first question to him, Trump told her "you're looking well. You're looking well."

With Ben Carson's exit from the race this week, the field of Republican candidates has now been narrowed to four, but any number of predictions that GOP voters would unite behind one anti-Trump candidate have come and gone without a change in the overall dynamic.

Trump, with 10 state victories, leads the field with 329 delegates. Cruz has 231, Rubio 110 and Kasich 25. It takes 1,237 delegates to win the Republican nomination for president.